Thyristor Amplifier Research Articles

Microcomputer as a Programmable Controller for State Feedback Control of a DC Motor Employing Thyristor Amplifier

A microprocessor-based state feedback control of a single-phase thyristor bridge/dc motor drive system is presented. Considering the drive system as a regulator problem in multivariable system theory, suitable control laws are developed using a state space model and applying a pole placement technique for fast regulation coupled with system stability by state feedback. To improve the response further, feedforward control is included in the control law so that the output follows the reference with minimum delay. A minimal order observer is also incorporated to make a quick estimate of the armature current (assumed to be inaccessible) from the knowledge of output speed and inputs of the system. Finally, the controller including the feedback control, feedforward control, and minimal order observer has been implemented in real time using an Intel 8085 microprocessor kit with suitable interfacing and standard software package. The experimental setup is fabricated and tested, and the test results are compared with digital simulation results for step changes in reference and load torque.

The application of an adaptive noninteracting controller to a motor-generator set

Relatively few experimental applications of decoupling theory to actual systems are recorded in the literature. It was decided, therefore, to examine a practical system consisting of a motor-generator machine set controlled by thyristor amplifiers, and to apply a decoupling strategy with adaptive properties to this system. A mathematical model of the coupled system was produced and validated from open-loop steady-state and transient characteristics. The system equations were arranged in state-variable form, and a strategy for decoupling this linearised system was developed theoretically and later confirmed by analogue simulation and actual system tests. It was then necessary to extend this linearised model theory to obtain a generalised nonlinear control strategy in terms of the system output variables; the elements of the feedback and feedforward matrices were made to adapt to the nonlinear effects within the system. Satisfactory decoupling of the appropriate state variables, together with eigenvalue assignment, was achieved both from the analogue simulation of the motor-generator model (linear and nonlinear) and upon the system itself incorporating transducer and equipment design. The results of the work have been engineered into an actual decoupled, adaptive motor-generator machine set.

A New Speed-Control System for DC Motors and its Application to Elevators

A circuit with a unidirectional armature current and bidirectional field current was used in order to realize a high-reliability speed-control system for dc motors by simplifying the armature circuit construction in comparison with conventional Thyristor-Leonard speed-control systems. In making the new circuit feasible, we developed a system in which either armature current or field current is fixed and the other varies depending on the magnitude of the torque command; a high-reliability magnetically controlled three-phase thyristor amplifier; and minor feedback loops provided with a field current control circuit and armature current control circuit. By using these techniques, we developed a dc motor control system that features higher reliability and smaller power consumption than conventional control systems. The new system was applied to elevator control with good results.

誘導負荷サイリスタ増幅器を含む閉ループ系の振動現象

誘導負荷サイリスタ増幅器を含む閉ループ系の振動現象

Integrated digital control of a multi-machine drive

The design and operation of an on-line computer controlled multimachine drive is described. The drive consists of ten fractional horsepower synchronous motors with compliant coupling between adjacent machines. The stators are supplied at 50 Hz and the rotors are excited by individual two-phase computer-fired thyristor amplifiers. The load angles are measured digitally and the computer can thus provide a closed loop multivariable control of the load angles and thus the drive tension. Computer-fired thyristor amplifiers have the advantage that digital-analogue convertors are not required and that very simple firing circuits can be used but in previous work little time was left for other calculations by the computer. In this present work this is overcome by introducing a moderate amount of external logic. Results are given for an optimal control of the drive which is shown to be straightforward to design and implement. Es wird die Konstruktion und den Betrieb eines Digital rechengerät geregeltes Mehrmaschinenbetriebsart beschreibt. Der System besteht auf zehn kleinen Synchronmoteren mit Federfesselungskraft zwischen nebenstehenden Maschinen. Die Ständerwicklungen werden um 50 Hz mitgeliefert, und die Läuferwindungen sind von einzelnen zweiphasenen von einen Rechengerät ausgelösten Thyristorverstärker erregt. Die Läuferstellungen sind ziffernmässig gemessen, und der Rechengerät kann deswegen eine Mehrgrossen - Regelung der Läufer Stellungen geben. Die Verstärker haben den Vorteil, dass man keinen Digital-Analog Anrichter braucht, auch dass sehr einfachen Kippkreise benutz werden können, während bei frühere Vorbilde blieb wenig zeit beim Rechengerät für weitere Rechnungen übrig. Dieser Problem ist bei diesem Vorbild von gewissen äusseren logischen Operationsgeräten gelöst. Es wird Ergebnisse für optimale Regelung des Systems gegeben.

サイリスタ増幅器を含む閉ループ系の1/2次調波自励振動

サイリスタ増幅器を含む閉ループ系の1/2次調波自励振動

Evaluation of core characteristics of magnetic phase shifters for thyristor amplifiers

The exciting current characteristic is suggested as a new method of evaluating the core characteristic. The phase shifting characteristic and the difference between a positive and negative waveform of a balanced half-wave type magnetic phase shifter are calculated by using the exciting current characteristics of cores employed in it. From these theoretical analyses, it can be determined that the difference of a positive and negative waveform is caused by a difference of exciting current characteristics of two cores used in it, and it becomes larger in proportion to larger control-circuit resistance. An experiment was performed using two pairs of cores, in which one pair of exciting currents are identical and the other pair differ. Theoretical results are in good agreement with the experimental results.

Automatic control system of the AMICOM 8000-kw plasma facility

A description is given of the control system for the MICOM 8000-kw plasma facility. This includes a set of six 65-kw, 3-phase, phase-controlled thyristor amplifiers which, together with control and digital multiplexing components, regulate the field currents of the six power generators in the plasma facility. Problems encountered in the design of the control system were related to the establishment of stability, accuracy (2%) and speed of response (system time constant «0.13 sec) in the facility. Sufficient details are given to permit a working understanding of the system's structure and design concepts.

High-speed pulse-width modulated thyristor amplifier for d.c. motor control

Abstract This paper is concerned with the development of a high-speed pulse-width modulated convertor for a d.c. motor drive in which linearity and fast transient response are prime requirements. Difficulties in thyristor commutation for currents of the order 50 amps at 2 kHz are discussed and special circuit features and design considerations to overcome these difficulties are presented. Test waveforms and overall experimental performance show the ability of the present convertor to control the torque of a d.c. motor with the required linearity and transient response. Further improvement in transient torquo response is achieved through armaturo current feedback. This is shown theoretically and experimentally. The addition of speed as well as current feedback around the convertor, can be used to control d.c. motor damping characteristics. The theory of damping control is given and experimental verification is shown in oscillograms.

State-transition analysis of certain thyristor systems

The operation of an m-phase thyristor amplifier with a fully inductive load is treated by state-variable methods. The amplifier and its associated system is treated as a non-conventional sampling system whose basic sampling interval is divided into two subintervals, with appropriate state and transition equations in each. An example is given for a simple current-control system.

Stability of first-order sampling and thyristor systems

Half-order subharmonic instability, which can occur in closed-loop systems containing an ideal sampler feeding a first-order load, does not occur when the sampler is replaced by a thyristor amplifier with the same d.c. gain. Analysis by the subharmonic describing-function method indicates that both systems are stable and so time domain analyses are presented which account for their behaviour.

Direct digital control of thyristor amplifiers

The direct digital control of thyristor amplifiers, in which each thyristor is directly under the control of the control computer, is described. This technique combines the normal advantages of computer control, such as a stored reference program, high accuracy steady-state control and the ability to calculate complex control functions, with those of full logical control of the amplifier. In addition, it dispenses with the need for a digital-analogue converter. A full description is given of the implementation of a computer-controlled 3-phase bridge amplifier in a closed-loop voltage control, including the individual addressing and firing of the thyristors from the accumulator of the computer, and other details of the control algorithm. Results are given from experiments with 2-, 3- and 6-phase star systems in addition to the 3-phase bridge system.

Ripple instability in closed-loop pulse-modulation systems including invertor drives

Describing functions at subharmonic frequencies are established for a range of pulse modulators. These allow an analysis to be made of the phenomenon of ripple instability in closed-loop systems containing such modulators, wherein the loop may oscillate at a submultiple of the fundamental frequency of the ripple in the modulator output. This basically occurs because the gain of the modulator at these subharmonic frequencies can be greater than its d.c. value. The modulation processes studied are pulse-length, pulse-position, pulse-width and pulse-amplitude modulation. It is shown for these cases that the gain of the modulator is enhanced most at the ½-order subharmonic, which, as a result, tends to be the dominant type of ripple instability. A particular application of these modulators in closed-loop systems which is of current interest is the thyristor invertor. In the second part of the paper the describing-function approach is developed to analyse the particular case of a d.c.-link invertor in a closed-loop system, e.g. a wide-bandwidth current-limit control in an invertor drive. It is shown to explain and predict the ripple-instability behaviour of the system, and good agreement is reached with analogue-computer results. The cases of fixed- and variable-frequency operation are investigated, together with the effects of utilising a thyristor amplifier in the loop to provide the d.c.-link voltage.

Ripple instability in closed-loop control systems with thyristor amplifiers

In a simplified analysis of thyristor amplifiers in closed-loop control systems, the amplifier is represented at all frequencies by its d.c. gain, and the effect of the output ripple voltage is neglected. This approach is inadequate for wide-bandwidth systems, and fails to predict the occurrence of ripple instability. A more accurate analysis is made in the paper, taking into account the sampling action of the amplifier in the presence of alternating component voltages in the loop. Ripple instability is characterised by the generation of continuous oscillations at a subharmonic of the balanced-amplifier ripple frequency, and manifests itself in the amplifier as a periodic variation in the firing pattern. The behaviour of an m-phase amplifier in an otherwise linear system of any order is investigated, and an exact analysis is given for subharmortic oscillations of order ½. At the ½-order, and other, subharmonic frequencies, describing functions are derived, and the amplifier response is seen to differ markedly from the simple assumption of constant gain at all frequencies. The describing-function technique is extended to evaluate phase margins which must be satisfied at the various subharmonic frequencies to prevent ripple instability, thus allowing a straightforward design technique based on conventional frequency-response methods. The results of the analysis are compared with experimental results from regulated power-supply systems, and good agreement is reached.